Opioids have known and reproducible effects on the human central nervous system, which principally include miosis, euphoria and analgesia. That certain strains of animal models have been bred to relatively more or less responsive to certain opioid agonists and antagonists suggests that individual differences in human opioids in humans have been documented. These data raise the question: In what manner, if any, do these individual differences relate to analgesic and euphorigenic responses on one hand, and the susceptibility to chronic pain syndromes or to opioid abuse on the other? The ultimate goal of this work, beyond completion of this pilot, is to learn if central opioid responsivity can predict aberrant responses to pain and opioids that contribute to maladaptive pain and addiction responses.